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Help! There are a bunch of dead fish in my pond, what happened?
Jason – Hastings, NE

The arrival of spring is an exciting time for pond owners. The weather is warming up, the sun is shining and the ice is melting away from the surface of your pond. Some pond owners however, find all of their fish floating dead at the water’s surface. While experiencing a winter fish kill is not the best way to start the season if you understand the cause you can prevent future occurrences.

Your pond is constantly absorbing and releasing air. As wind blows across the surface of the pond water ripples absorb oxygen into the water column. Decomposing organic debris at the bottom of the pond release a gas that floats to the surface of the pond where it is released into the atmosphere.

The layer of ice that forms over your pond blocks air exchange locking fresh oxygen out of the pond and harmful gas from decomposition in. Depending on the size of the pond and the amount of decomposing debris available, your fish can be overwhelmed and killed by the lack of fresh air.

Fish kills can also happen in the summer. Summer fish kills are typically caused by pond turnovers due to lack of proper aeration. The top layer of water in your pond carries more oxygen and reacts faster to temperature changes due to its exposure to the air. The bottom of your pond will tend to contain less oxygen, light and will be slower to warm up throughout the summer. These layers of water are referred to as stratification and are divided by thermoclines. If you have ever swam in your pond you may have noticed that your feet are colder than your chest as they break the thermocline in the water column. Your fish will find a happy medium in the water column where there is adequate oxygen and warmth.

Particular rainy or windy days can cause the thermocline in your pond to break. The bottom layer of water in your pond will mix together with the healthier top layer of water. As your fish have nowhere to flee to, they are trapped in the newly mixed pond water which can severely stress and even kill your fish.
Fortunately, there are a couple of ways to prevent winter and summer fish kills. An Bottom Diffused Aeration System like the Airmax® Pond Series™ pumps fresh air to the bottom of your pond and breaks it into fine bubbles that can be absorbed into the water column. As the air bubbles rise through the water column they also circulate the water body making sure that your pond is evenly oxygenated and warmed. An abundance of oxygen promotes the presence of beneficial aerobic bacteria which will help break down organic waste faster and without the egg-like odor produced by the slow anaerobic bacteria in water that lacks oxygen. Running an aeration system in the winter can also eliminate your winter fish kills as the constant bubbling at the surface of your pond prevents ice formation and quickly breaks up layers of ice.

To further aid in your fish kill prevention, you will want to remove as much organic debris from the bottom of the pond as possible. Beneficial Bacteria products like PondClear™and MuckAway™ in tandem with EcoBoost™ will naturally digest gas and algae causing muck without having to chemically treat your pond. Cut down and drag away any dead cattail reeds and leaves with a Weed Cutter and Rake so that they are not left to decompose. The Pond Logic® ClearPAC® PLUS combines all the beneficial bacteria products you need along with pond dye and an option algaecide to eliminate the guesswork of selecting the proper pond care products.

Pond Talk: Did you find any surprises under the ice in your pond this spring? What are you doing to resolve the issue?

One Response

I’m new to this but I’ve always been interested. I just read that here in New Hampshire Pastor Livingston Stone started one of our first trout ponds in 1866. This is the best site I’ve found so far on this topic. Thanks